1. Field of Invention
The present invention relates generally valves which are operable to control the flow of pressurized fluids to a blowout preventer in offshore oil or gas wells. In particular, the invention relates to a sub plate mounted (SPM) valve that is selectively movable between an armed configuration and a disarmed configuration, and is adapted for maintaining operable stability in both the armed and disarmed configuration.
2. Description of Related Art
Valves used in hydrocarbon recovery operations include SPM valves for controlling the flow of pressurized fluid to a blowout preventer. Although these valves are typically referred to as sub plate mounted valves, the particular mounting position for these valves may vary between applications.
Various types of SPM valves have been developed including 2-way and 3-way valves. One common design for SPM valves includes a valve housing with an open interior defining a longitudinal axis. The open interior is fluidly communicable with a supply port, a discharge port, and often with a vent port as well. A spool is selectively movable through the open interior, along the longitudinal axis, to control fluid flow between the supply port and the discharge port. The spool can be moved to a first position within the open interior wherein fluid is permitted to flow between the supply port and the discharge port thereby arranging the valve in an “armed” configuration. The spool can also be moved to a second position within the open interior where fluid is prevented from flowing between the supply port and the discharge port thereby arranging the valve in a “disarmed configuration.” Thus the valve is operable to arm and disarm hydraulic circuits, which may include additional valves for operating the ram of a blowout preventer.
Many of the valves of this type include springs to bias the spool to one of the first and second positions. The spool is generally movable to the other of the first and second positions by providing a pilot pressure to a pilot port of the valve. Other valves are double-piloted and require a pilot pressure to be maintained at one of two pilot ports to maintain the spool in a particular position within the open interior. Fluid flowing through the spool of these valves often serves to counteract the spring bias or the pilot pressure, and thus, the spool can be unstable and shift to an unintended position.